1. Field of the Invention
The invention relates generally to devices for use with valve means included within a fluid flow system.
2. Disclosure of Related Art Including Information Disclosed Under 37 C.F.R. .sctn.1.97-1.99
A wide variety of fluid flow systems are known and used in commerce and industry. Many of those systems contain non-compressible fluids which flow through them. When the fluid flow system is an enclosed system, there is a need to prevent the flow of such a non-compressible fluid from being stopped rapidly, such as by the rapid closing of a valve or a similar device. Rapid valve closure often results in the generation of a shock wave, which manifests itself as "water hammer" and other related problems. In fact, the shock wave resulting from rapid valve close can produce a significant pressure surge which may exceed the design limit of one or more of the components comprised within the fluid flow system.
An example of the seriousness of this problem is that encountered in fire service systems, where water flows through system components ranging from pumps to valves to hoses of rubberized fabric or other composition to nozzles. If a valve in a fire service system is closed too rapidly, the shock wave may overwhelm the containment ability of system components, particularly the fire hose. A burst or partially pierced hose may result, which may throw the fire fighter off his feet or may pull free from his grasp, to whip or flail through the air, with resulting injury to that fire fighter, other nearby fire fighting personnel and/or bystanders. The high pressure under which water is pumped through a standard fire service system produces a water stream which itself, if freed from the hose or other system components in an unintended direction, can cause serious injury. Additionally, these shock waves or pressure surges can cause extensive damage to the main valving and/or pumps of a fire fighting vehicle, such as a pumper, which could disable the pumper without warning, stopping the flow of water to control a fire with the likely result of property loss and injury to human life and limb.
Many attempts have been made to control and/or prevent rapid valve closing and the resulting production of shock waves. The simplest method is merely to slowly close any valve comprised within a system in which a non-compressible fluid is flowing. In the heat of fighting a fire, when closing off a valve to prevent fluid flow in an unintended direction, remembering to close that valve slowly is usually not foremost in the mind of the individual interacting with the system.
Mechanical checks and protections to provide pressure relief if a shock wave is generated through too-rapid valve closing have been used to avoid the problem. Pressure relief means have long been the favored apparatus applied in these efforts, but the known pressure relief means are far too slow in their action. The shock wave will have already done its damage to the system by the time a pressure relief means senses the problem and releases the pressure. Pressure relief means also suffer from the inherent venting to the environment of the non-compressible fluid. If the fluid is water, that may not present an insurmountable problem, if proper drainage from the relief valve can be provided. If the fluid contains chemicals or is itself hostile to persons or the environment, pressure relief means are unacceptable and cannot be used.
The most popular mechanical checks and protections have tended to be those which somehow prevent too-rapid valve closing, while allowing the valve to be closed at a rate which will not produce a shock wave.
Blackman et al. U.S. Pat. No. 3,422,843 ("Blackman '843"), discloses a mechanism for swing type check valves, in which a fixed restraining or cushioning pressure is produced by the swinging closed of the valve to apply pressure to fluid in a chamber, thereby preventing the sudden impact of the valve with the valve seat. Swing valve 24 of the swinging disk type is supported on a swing arm 26, which has an enlarged, cylindrical end portion 28, whose axis is disposed at right angles to the direction of swinging movement of the valve. Within that end portion are diametrically opposed, inwardly extending vanes 30. A central shaft 34 extends longitudinally through part 28, and is connected to the valve casing 10. Shaft 34 bears diametrically opposed, inwardly extending vanes 36, which are in turn positioned within part 28 between vanes 30 thereof. The cylindrical part 28 is closed by bushings 38, with 0-rings 40, which, in cooperation with part 28 and shaft 34, forms an internal pressure chamber 42. Chamber 42 is divided into two sections by vanes 30, which are interconnected by restricted passageways 44, through which fluid may flow from one section past vanes 30 to the other, as the valve 24 swings closed. Each of vanes 36 comprise a bypass passageway 46 and a check valve 48, which closes that passageway against the flow of fluid during closing movement of swing valve 24 but which opens to allow free flow of fluid therethrough during opening movement of the valve.
Chamber 42 is filled with oil. As the valve moves to the open position, through the pressure of fluid flowing through inlet 12 and outlet 14 of the valve, the oil flows through passageways 46, providing little or no restraint to the opening of the valve. On back flow through the flow line, however, the back flow of oil in chamber 42 through passageways 46 is resisted by valves 48. The oil must flow through restricted passageways 44, thereby restraining the movement of the valve to prevent slamming on seat 18.
Blackman discloses as a critical portion of his device a cylindrical part 50, which is designed to prevent the rise of pressure in pressure chamber 42 from causing leakage or disruption of seals 40. Part 50 is attached to part 28 so as to extend laterally therefrom to form an auxiliary chamber 52, which is in communication with chamber 42. Piston 58 is movably disposed in chamber 52, and biased toward part 28 by a coil spring 66. When a high pressure is exerted on valve 24, which might damage seals 40, the pressure in chamber 42 causes piston 58 to move away from part 28, increasing the volume of the device so that the pressure does not exceed a predetermined maximum.
Unfortunately, the Blackman '843 device, as disclosed by the drawings, in particular FIG. 2, does not appear to be operative. From the relationship between fixed central shaft 34, valve swing arm 26, internal pressure chamber 42; longitudinal vanes 36 and vanes 30, the valve must be in the closed position in FIG. 2 (see col. 3, 11. 61-62). (It cannot rotate clockwise from that position, because longitudinal vanes 36 will almost immediately contact and be stopped by vanes 30). In the closed position, the chamber 42 is not connected to the pressure side of the fluid, indicating that the chamber does not do anything to relieve pressure at the end of the stroke, when the pressure would be highest.
The Blackman '843 device, even assuming its operability, has several severe shortcomings. The passage 46 / ball 48 check valves of Blackman '843 are one way only, such that the vane 30 / longitudinal vanes 36 system will provide restriction and hence protection in one direction only. The orifice or restriction provided by passageway 44 is fixed, such that no adjustment in pressure may be made without dismantling the unit, and removing and replacing a first central shaft 34 with a second shaft 34 having a differently sized/configured restrictive passageway.
Blackman '843's one way only resistance and lack of pressure/resistance adjustability is particularly disadvantageous in fluid flow systems used in fire service. Even if a Blackman '843 device could be adapted for use in a hose, the lack of resistance in valve opening leads to poor valve control practices which are both inefficient to fire fighting practices and potentially dangerous. The lack of ready pressure/resistance adjustability is a more serious lacking, particularly in a hose application, because various pump flow rates and pressures will render a fixed resistance either too great or, more often, too slight, defeating the intended ability to avoid shock wave and water hammer by failing to sufficiently slow valve closing. Too slow a valve close, in a fire hose application requires the firefighter to hold his physical position until flow ceases, for what may prove to be a period of time that exposes him to unacceptable danger and risk of injury. (Movement of a fire hose flowing water is extremely difficult and can in itself be quite dangerous).
Additionally, Blackman '843 is restricted in application to internal placement in a swing-type check valve configuration. A number of other valve constructions do not present any compatability with a Blackman '843 structure. The required internal placement of the Blackman '843 device, in particular view of the need to anchor central shaft 34 at opposite ends to a valve casing, such as casing 10, is a substantial drawback. Retrofitting of existing valves with a Blackman '843 device is impossible in view of the internal placement requirement.
The art, then, lacked apparatus capable of providing a controlled, slow close capability to valves in fluid flow systems requiring adjustability to the pressure/resistance presenting during valve closing. It also lacked apparatus presenting two way pressure/resistance to valve opening and valve closing, even without the desired adjustability of that resistance. Further, no such device of any structure was known which could be easily retrofitted to existing valves of a variety of structures. No apparatus or device offered the desired combination of these features: two way pressure/ resistance to valve opening and closing, ready adjustability of the magnitude of the pressure/resistance, and easy retrofitting capability to a variety of valve structures.
A long felt need in the art existed for apparatus which solved the problem of controlling water hammer and/or shock waves resulting from closure of valve means in a fluid flow system. As exemplified by the Blackman '843 device, no known apparatus had even one, let alone all, of the aforenoted optimal advantages and characteristics.